Protecting device for x-ray apparatus



Lulu- Jan. 26, 1954 A. KUNTKE ET AL 2,667,587

PROTECTING DEVICE FOR X-RAY APPARATUS Filed Dec. 1, 1951 INVENTORSALFRED K N K HEINZ MES FER AGENT Patented Jan. 26, 1954 PROTECTING;DEVICE FOR X-RAY APPARATUS Alfred Kuntke, Hamburg-Wellingsbuttel, and

Heinz Mester, Hamburg, to Hartford National Bank Germany, assignors andTrust Company,

Hartford, Conn., as trustee Application December 1, 1951, Serial No.259,408

Claims priority, ap

December 4 Claims.

Improvements in or relating to X-ray apparatus for diagnosis In X-rayapparatus the operating voltage i. e. the potential difference betweenanode and cathode of the X-ray-tube during normal operation is muchlower than the no-load voltage, since voltage losses occur in theapparatus and supply mains upon loading it. On putting an X-rayapparatusinto operation first the current for heating the incandescent cathode isswitched on, the high-voltage being applied after the cathode has beenheated. The loading current directly rising to its full value preventsthe voltage of the tube from becoming too high.

Application of the high voltage when the cathode is cold orinsufiiciently heated may cause break-down of a supply conductor,sparking in the envelope of the tube or damage to the X-ray tube.Consequently, care must be exercised, particularly according as thevoltage used is higher and if, since the size is preferably minimized,the apparatus is incapable of withstanding the noload Voltagecorresponding to the maximum permissible operating voltage.

Overvoltages may also be produced by mains voltage variations andtransient phenomena, but particular switching means generally permit ofavoiding them, without avoiding however the production of overvoltagesin taking X-ray exposures due to the absence of the expected andpreviously adjusted tube current. This may be caused by interruption ofthe heating circuit or by shortcircuits. It might be attempted to inferfrom the primary heating current the data required for detecting a faultin the heating circuit, but this is not very reliable owing to theslight difference between the no-load current strength and the strengthof the loading current of the heating transformer.

The present invention has for its object to prevent the X-ray apparatusfrom being connected into circuit in the absence of emission of theincandescent cathode in X-ray tubes. It concerns X-ray diagnosisapparatus comprising a circuit supplying a voltage which is lower thanthe normal supply voltage and, with the heating circuit cut in, issupplied to the primary of the highvoltage transformer, the dischargecurrent resulting from emission of the incandescent cathode operating adevice and the apparatus being adapted to be connected into circuit fortaking an exposure after said device has been made operative.

The low voltage preferably has a value at which the X-ray tube works inthe space charge range plication Germany at the high voltage end of thetransformer. Frequently, different current intensities and sometimesdiiierent X-ray tubes must be used. it being advantageous duced onapplying the voltage is substantially independent of the adjustedheating current.

The resistance of an X-ray tube, which is practically infinite in theabsence of cathode-emission, is of the order of 1 to 2 megohm in thespace charge range. The impedance diiference is sulficient to changeover a relay of a relay tube at the earthed centre of the secondarywinding of the high-voltage transformer.

Ii the transformer ratio of the high-voltage transformer is chosen to beapproximately to 290, the resistance variationof the X-ray tube reducesthe impedance at the primary side from about 10 ohms to about 200 ohms.This impedance variation is suflicient to provide for the desiredprotection at the primary side by means of an alternating current relay.The low voltage circuit may include the exciter winding of such a relayand this winding may, by the action of the supply current, close a relaycontact closing an interruption in a circuit including the exciterwinding of an electromagnetic switch for connecting the highvoltage-transformer to the nor mal supply voltage.

In order that the invention may be readily carried into efiect it willnow be described in detail with reference to the accompanying drawingi1lustrating two examples of circuit-arrangements for apparatusaccording to the invention, and in which a Fig. 1 shows the use ofprotective means at the primary side of the transformer.

Fig. 2 shows them at the secondary side.

An autotransformer 3 is connected by wayof main switch 2 to terminals Iof the A. C. mains.

This transformer supplies the normal voltage through a regulatingcontact for the high-voltage transformer 4 and is connected throughsupply conductors t, l to the primary winding 5. Supply conductor 6includes a switch arm 8 and supply conductor I may also comprise such anarm 9.

These switch arms form part of an electromag-.

netic switch it and are open if the apparatus is inoperative. A.secondary winding II is connected to an X-ray tube I5 comprising ananode l4 and an incandescent cathode i3, according to Fig. l with theinterposition of rectifiers l2.

The cathode it of X-ray tube I5 is supplied from a heating transformerI6, whose primary comprises the regulating resistor I 1 for adjustingthe heating current.

that the current strength pro- In Fig. 1 an electric circuit connectedto the mains-voltage includes a switch I8 adapted to occupy threepositions 0, I, 11. In position 0 there is no flow of current. Inposition I, current is supplied to an exciter winding IQ of the relay sothat the movable contact 20 completes the circuit connecting theauxiliary winding 2| of autotransformer 3 to the primary 5 or thehigh-volt age transformer 4. The voltage supplied by this. winding has avalue lower than that supplied by autotransformer 3. After switch 2 hasbeen closed and no deviation occurs in the heating current, the X-raytube passes current by which the low voltage winding 2| is loaded. Theloading current passes through an exciter winding 22 of anelectromagnetic relay and closes contact 23 of a circuit including atime switch 24 and the- In position II of switch winding of switch H).18 this circuit is closed. Besides switch arms 8 and 9 the winding l0operates a switch arm 2'! interrupting the low-voltage circuit and aswitch arm 26 shunting the contact 23. The trans former 4 is connectedto the normal supply voltage by connecting the arms 8 and 9 intocircuit. The duration of the load is adjusted by means of the timeswitch 24, the latter subsequently interrupting the current so thatswitch I0 is released.

If, however, the incandescent cathode I3 of X-ray tube l5 does not emit,for example, due to a short-circuit or a defective cathode, theimpedance transformed on to the primary circuit is such that nosufiiciently strong current passes in the low-voltage circuit to exciterelay wind ing 22. Contact 23 remains open and switch H3 remainsinoperative.

This also holds in Fig. 2, wherein the exciter Winding 22 for contact 23is included in the anode circuit of a relay tube 33 comprising a sourceof anodevoltage 35 Relay tube33 comprises an earthed cathode 34 at thegrid 32; which is connected to a point of resistor 30. This point may bedisplaceable to permit adjustment of the instant at which the anodecurrent is suificiently strong to energise winding 22 in accordance withthe emission of the cathode l3 of the X-ray tube.

The resistance 30 is connected throughrectifier 29 to the ends ofresistor 28 at the centre of the secondary l I of the high-voltagetransformer.

In parallel with this resistor is connected another rectifier 3| so thata rectified current passes through resistor 30. The center of resistor 28v is connected to earth.

The operation of the device corresponds to that shown in Fig. 1.

What we claim is; r

1. An X-ray diagnostic apparatus comprising an X-ray tube includin ananode and meandescent cathode, a high-voltage transformer coupled tosaid tube and including a primary winding, first means for applying, aheating current to said cathode, second means for applyingv a givenoperating potential to the primary winding of said transformer, thirdmeans for applying a potential which is lower than said given poten--tial' to the primary winding of said transformer, firstcurrent-responsive means coupled to saidv tube and responsive to thecurrent flow therethrough when said lower potential is applied to saidprimary winding, second current-responsive means responsive to actuationof said first ourrent-responsive means when emission from said cathodereaches a given value for connecting said second means, to said primarywinding, and timing means operatively associated with said secondcurrent-responsive means for determining the duration of the applicationof said given operating potential to said primary winding.

2;. 'An X ray diagnostic apparatus comprising an X-ray tube including ananode and incandescent cathode, a. high-voltage transformer coupled tosaid tube and including a primary winding, first means for applying aheating current to said cathode, second means for applying a givenoperating potential to the primary winding of said transformer, thirdmeans for applying a potential which is lower than said given potentialand at which the X-ray tube will operate in the space charge region tothe primary winding of said transformer, first current-responsive meanscoupled to said tube and responsive to the current flowtherethroughwhen. said lower potential is applied to said primary winding, secondcurrent-responsive means responsive to actuation of said firstcurrent-responsive. means when emission from said cathode reaches agiven value for connecting said second means to said primary winding,and timing means operatively associated with said secondcurrentresponsive means for determining the duration of the applicationof said given operating potential to said primary winding;

3. An X-ray diagnostic apparatus comprising an X-ray tube including ananode and incane descent cathode, a high-voltage transformer" coupled tosaid tube and including a primary winding and a center-tapped secondarywinding, first means for applying a heating current to said cathode,second means for applying a given operating potential to the primarywinding of said transformer, third means for applying a potential whichis lower than said given'potenti'al and at which the X-ray tubewilloperate in the space charge region to the primary windin iof saidtransformer, first current responsive means coupled to said tube and thecenter tap of said secondary windingand responsive to the current flowthrough said tube when said'lower'potential" is applied to saidprimarywinding, second current-responsive means" responsive toactuation" of said first current-responsive means when emission fromsaid cathode reaches a given valuefor connecting said second'means tosaid primary winding, and timing means'operatively; as-'-- sociated withsaid second current-responsive means for determining the duration of theap;-- plication of said given operating potential to said primarywinding.

4. An- X ray diagnostic apparatus as claimed in claim 3' in which saidfirst current-responsivemeans is an electric discharge tube.

ALFRED KUNTKEZ HEINZ' MESTER.

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2,100,735 Dawson.v ;.Nov-. 30, 1937- 2,2-15,'744 Silbermanns.Sept..24,-.l940, 2,244,137 Bischofi, et a1. June,-3, 194-1,

' 2,512,193 Zavales June 20, 195.0-

